convert ajax actionlink as a bootstrap button

You should be able to use the htmlAttributes parameter to add whatever Bootstrap class you want:

@Ajax.ActionLink("EMPLOYEE", "_PartialEmployeeIndex", "Employee", new AjaxOptions() { UpdateTargetId = "divToUpdate" }, new { @class = "btn" })

If you only want an icon you can do it as:

    @Ajax.ActionLink(" ", "Delete", new { id = 1 }, new AjaxOptions
                                        {
                                            Confirm = "Are you sure you wish to delete?",
                                            HttpMethod = "Delete",
                                            InsertionMode = InsertionMode.Replace,
                                            LoadingElementId = "div_loading"
                                        }, new { @class = "glyphicon glyphicon-trash" })

• The name ationlink cannot be null or empty, so i recommended an space.

If you want an actual Ajax button element, rather than a styling hack, it is also possible but a little involved. It is a shame that MS has not yet chosen to add an ActionButton to both the Html and Ajax helpers as the differences are actually very minor when you remove the duplication of private support methods (you would only need the ActionButton and GenerateButton methods shown below).

The end result is you can have real buttons that trigger like ajax action links:

e.g.

@Ajax.ActionButton("Delete", "Delete", "document", 
     new { id = ViewBag.Id }, 
     new AjaxOptions() 
     { 
         Confirm="Do you really want to delete this file?", 
         HttpMethod = "Get", 
         UpdateTargetId = "documentlist" }, 
         new { id = "RefreshDocuments" 
     })

1. Create an AjaxHelper extension

The code below is based on a decompile of the AjaxExtensions class as many of the required helper methods are not exposed on HtmlHelper.

public static partial class AjaxExtensions
{
    public static MvcHtmlString ActionButton(this AjaxHelper ajaxHelper, string buttonText, string actionName, string controllerName, object routeValuesBlah, AjaxOptions ajaxOptions, object htmlAttributesBlah)
    {
        // Convert generic objects to specific collections
        RouteValueDictionary routeValues = new RouteValueDictionary(routeValuesBlah);
        RouteValueDictionary htmlAttributes = HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributesBlah);

        if (string.IsNullOrEmpty(buttonText))
            throw new ArgumentException("Button text must be provided");
        string targetUrl = UrlHelper.GenerateUrl((string)null, actionName, controllerName, routeValues, ajaxHelper.RouteCollection, ajaxHelper.ViewContext.RequestContext, true);
        return MvcHtmlString.Create(GenerateButton(ajaxHelper, buttonText, targetUrl, AjaxExtensions.GetAjaxOptions(ajaxOptions), htmlAttributes));
    }

    public static string GenerateButton(AjaxHelper ajaxHelper, string linkText, string targetUrl, AjaxOptions ajaxOptions, IDictionary<string, object> htmlAttributes)
    {
        TagBuilder tagBuilder = new TagBuilder("input");
        tagBuilder.MergeAttribute("value", linkText);
        tagBuilder.MergeAttributes<string, object>(htmlAttributes);
        tagBuilder.MergeAttribute("href", targetUrl);
        tagBuilder.MergeAttribute("type", "button");
        if (ajaxHelper.ViewContext.UnobtrusiveJavaScriptEnabled)
            tagBuilder.MergeAttributes<string, object>(ajaxOptions.ToUnobtrusiveHtmlAttributes());
        else
            tagBuilder.MergeAttribute("onclick", AjaxExtensions.GenerateAjaxScript(ajaxOptions, "Sys.Mvc.AsyncHyperlink.handleClick(this, new Sys.UI.DomEvent(event), {0});"));
        return tagBuilder.ToString(TagRenderMode.Normal);
    }

    private static string GenerateAjaxScript(AjaxOptions ajaxOptions, string scriptFormat)
    {
        string str = ajaxOptions.ToJavascriptString();
        return string.Format((IFormatProvider)CultureInfo.InvariantCulture, scriptFormat, new object[1] { str });
    }

    private static AjaxOptions GetAjaxOptions(AjaxOptions ajaxOptions)
    {
        if (ajaxOptions == null)
            return new AjaxOptions();
        else
            return ajaxOptions;
    }

    public static string ToJavascriptString(this AjaxOptions ajaxOptions)
    {
        StringBuilder stringBuilder = new StringBuilder("{");
        stringBuilder.Append(string.Format((IFormatProvider)CultureInfo.InvariantCulture, " insertionMode: {0},", new object[1]
        {
             ajaxOptions.InsertionModeString()
        }));
        stringBuilder.Append(ajaxOptions.PropertyStringIfSpecified("confirm", ajaxOptions.Confirm));
        stringBuilder.Append(ajaxOptions.PropertyStringIfSpecified("httpMethod", ajaxOptions.HttpMethod));
        stringBuilder.Append(ajaxOptions.PropertyStringIfSpecified("loadingElementId", ajaxOptions.LoadingElementId));
        stringBuilder.Append(ajaxOptions.PropertyStringIfSpecified("updateTargetId", ajaxOptions.UpdateTargetId));
        stringBuilder.Append(ajaxOptions.PropertyStringIfSpecified("url", ajaxOptions.Url));
        stringBuilder.Append(ajaxOptions.EventStringIfSpecified("onBegin", ajaxOptions.OnBegin));
        stringBuilder.Append(ajaxOptions.EventStringIfSpecified("onComplete", ajaxOptions.OnComplete));
        stringBuilder.Append(ajaxOptions.EventStringIfSpecified("onFailure", ajaxOptions.OnFailure));
        stringBuilder.Append(ajaxOptions.EventStringIfSpecified("onSuccess", ajaxOptions.OnSuccess));
        --stringBuilder.Length;
        stringBuilder.Append(" }");
        return ((object)stringBuilder).ToString();
    }

    public static string InsertionModeString(this AjaxOptions ajaxOptions)
    {
        switch (ajaxOptions.InsertionMode)
        {
            case InsertionMode.Replace:
                return "Sys.Mvc.InsertionMode.replace";
            case InsertionMode.InsertBefore:
                return "Sys.Mvc.InsertionMode.insertBefore";
            case InsertionMode.InsertAfter:
                return "Sys.Mvc.InsertionMode.insertAfter";
            default:
                return ((int)ajaxOptions.InsertionMode).ToString((IFormatProvider)CultureInfo.InvariantCulture);
        }
    }

    public static string EventStringIfSpecified(this AjaxOptions ajaxOptions, string propertyName, string handler)
    {
        if (string.IsNullOrEmpty(handler))
            return string.Empty;
        return string.Format((IFormatProvider)CultureInfo.InvariantCulture, " {0}: Function.createDelegate(this, {1}),",
            new object[2]
              {
                propertyName,
                handler
              });
    }

    public static string PropertyStringIfSpecified(this AjaxOptions ajaxOptions, string propertyName, string propertyValue)
    {
        if (string.IsNullOrEmpty(propertyValue))
            return string.Empty;
        string str = propertyValue.Replace("'", "\\'");
        return string.Format((IFormatProvider)CultureInfo.InvariantCulture, " {0}: '{1}',",
            new object[2]
              {
                propertyName,
                str
              });
    }
}

2. Modify jquery.unobtrusive-ajax.js

Only a small change is required to the JQuery of jquery.unobtrusive-ajax.js to accept the new button object, as it is very close to begin with. First the selector needs to accept buttons as well as links and then the href needs to come from an attribute so than a non-link can provide it (not strictly browser compliant but works for now).

$(document).on("click", "input[data-ajax=true],a[data-ajax=true]", function (evt) {
        evt.preventDefault();
        asyncRequest(this, {
            url: $(this).attr("href"),
            type: "GET",
            data: []
        });
    });

*Note: this is using the latest version of everything as at the date of answering (MVC 5)